Why does the diode behave like a short circuit?

[kbjee]

I have a diode where the mesa structure has layers as follows-

material 1(P+)
thin region (10nm) of material 2(P-) different badgap
material 1(N-)
material 1 (N+).

Overall it is a PIN structure. All materials are narrow bandgap, in mid IR region (~300meV).
When I measure I-V, I get a more-or-less straight line. The resistance is tens of ohms. The device behaves as if there is no P-N junction. I have earlier worked with a similar structure without the thin region and that gives good R0A values.

Do you have any idea why this might happen? I had some ideas but looks like those are not the right reasons according to further experimentation.

 

[IRstuff]

oops: "Gold usually, and even ALUMINUM sometimes"

TTFN

FAQ731-376

 

[IRstuff]

If you think about it, it makes sense. An unalloyed metal/semiconductor junction tends to become a Shottky barrier diode, so the only way out of that is to alloy the materials together. Therefore, the contact always has some level of interdiffusion between the two materials.

Overalloying, or overcurrent, can cause the diffusion to reach far enough to snuff the junction.

TTFN

FAQ731-376

 

[IRstuff]

This is somewhat testable. I'm not too up on the procedures, but removal of the metallization and doing smoe crystal etching should reveal pits, if overcurrent, at least in silicon. Unclear what overalloying might look like, though.

TTFN

FAQ731-376

 

[kbjee]

Thanks for the suggestions.